The present invention relates to electroluminescent devices (hereinafter referred to as EL devices), especially organic thin-film EL devices, useful for displays, and to processes for producing the same.
There is a great deal of interest in the application of EL devices to spontaneous-emission panel displays. In particular, organic thin-film EL displays using organic substances as luminous materials emit light of high luminance even at low applied voltages of not more than 10 V, and thus show excellent luminous efficiencies. Moreover, these displays can emit light even when the EL devices used have simple structures. There is therefore such a hope that organic thin-film EL displays be applied to high-resolution full-color displays, or to inexpensive simple displays that are used for displaying fixed patterns for advertisement or the like by the emission of light.
The production of displays using EL devices practically requires the patterning of electrodes and of organic EL layers, and typically includes a photolithographic process, or a patterning process using a complicated system for pattern-wise depositing films. Such production processes are complicated, and bring about increase in production cost. Further, a process in which an organic EL film is formed pattern-wise by deposition using a mask requires a vacuum apparatus, which is expensive. Problems with this process are decrease in yield, and increase in cost. On the other hand, a process in which patterns are formed by an ink jet process includes steps that are relatively simple; however, this process has the problems of decrease in yield and in evenness of film thickness. In addition, EL devices for displaying patterns for advertisement are required to take various shapes and to have greatly increased surface areas. The production of such EL devices is confronted with the problem of remarkable decrease in productivity.
Thus, the production of EL devices, especially that of organic EL displays, includes the patterning of electrodes, organic EL layers, insulating layers, etc., so that it inevitably includes a considerably great number of steps. The production of EL devices, therefore, has problems awaiting solution on yield, productivity and cost. In addition, it is important to increase the pattern accuracy of a luminous layer in order to improve displaying properties, so that it is necessary to accurately provide, on an electrode, a luminous layer with a uniform thickness.
An object of the present invention is to provide an EL device that can be produced more simply than ever, and a process for producing the same; in particular, an EL device whose constituent layers such as a luminous layer and a partitioning layer have excellent pattern accuracy and which emits light with high uniformity, and a process for producing such an EL device.
We found that the aforementioned problems in the prior art can be solved by applying light pattern-wise to a layer of a material whose wettability changes when light is applied thereto, thereby forming on the layer a latent pattern due to the difference in wettability, and then forming an EL layer, a partitioning layer, an insulating layer, a first electrode, a second electrode, etc. by utilizing this latent pattern. The present invention was accomplished on the basis of this finding.
Accordingly, the present invention is an EL device comprising a first electrode, an EL layer formed on the first electrode, and a second electrode formed on the EL layer, characterized by being provided with at least one layer of a material whose wettability changes when light is applied thereto.